The internal combustion engine (ICE) is generally the main source of traction power in a conventional vehicle. Fuel is injected into the cylinders of the ICE and is ignited, which displaces the piston resulting in a reciprocating movement and, consequently, a rotating crankshaft torque and speed output. The ICE has the capacity to accelerate a vehicle to a high speed within seconds, thereby giving the best in driving experience and maneuverability. However, such mechanical power transfer results in a relatively low engine efficiency, typically about 20–30%.
The ICE generally performs optimally and at best efficiency if the speed and torque output demands do not vary extensively, i.e., the ICE is more efficient at a constant speed and torque operation. Generally, the more speed or torque changes that occur, the lower the efficiency of the ICE. A typical example is during acceleration. One reason for low efficiency is that during a high rate of change in speed demand a large amount of fuel is injected into the cylinders and ignited, but not all of the fuel is burnt. In addition, a significant portion of the fuel is partly burnt. Therefore, more fuel is consumed than actually required for a stated acceleration. The inefficient burn generally leads to higher emissions of NOx, CO, and hydrocarbon particulate matter. Also, during acceleration additional torque is required by the ICE itself to accelerate various engine components to overcome friction and nonlinear hydrodynamic forces in the cylinders. These factors tend to increase fuel consumption and emission levels, and reduce the response time and, hence, the acceleration rate.
Hybrid electric vehicles use an ICE and an electric motor in combination for traction application with a defined hybridization factor. The use of the electric motor, which is a dynamic system, provides better response to torque and speed demands. In many hybrid electric vehicles, the electric motor provides the initial traction power output, often referred to as “electric launch assist,” and, after a predefined speed level, the ICE and the electric motor together aid in providing traction. The electric motor provides a direct traction support to accelerate the vehicle. The electric motors for accelerating a vehicle are relatively large machines having capacities of 10 kilowatts and higher. In addition, the electrical power for operating an electric motor is supplied by high capacity battery pack, such as having a high voltage of 100 volts, or higher.
Over the past few decades, the overall power demand in automobiles has been increasing. Until recently, the electrical loads in automobiles were typically a few lighting loads and a starter motor. However, the current safety and entertainment loads that are now becoming typical and/or standard vehicle equipment impose a high level of load demand on the typical 12 volt system. Also, traditional pneumatic, hydraulic, and mechanical driven loads are often being replaced by electrical systems for improved performance, efficiency, and reliability. This transition brings about the concept of “Power on Demand,” making power available when required. The average power demand in near-future vehicles is expected be about 5 kilowatts and the peak demand will be as high as about 12 to 15 kilowatts. Performance loads such as an electromagnetic valve train (EVT), which have power requirements that increase from about 1 kilowatt to 4 kilowatts with speed, and electric steering systems that have peak loads of about 1.5 kilowatts, will impose higher demands on vehicular power system.
The current power generation systems in automobiles, such as the conventional production alternator, can typically generate power efficiently up to about 1.5 to 2 kilowatts. Attempts to generate higher power often result in substantial power loss and unacceptable cooling requirements, thereby lowering system efficiency. Integrated Starter/Alternators (ISA) are being developed as an alternative electrical power solution that provides high power both efficiently and reliably. The ISA is essentially a single machine performing the function of both the starter motor and alternator.
The ISA is an electromagnetic motor/generator that is connected directly to the crankshaft of the ICE. The ISA machine generally has a stator and a rotor like any other electric machine. The rotor of the ISA is often placed directly on the crankshaft while the stator is fixed to the body of the ICE. The rotor on the crankshaft can eliminate belt and gear engagement mechanisms and their associated losses and wear and tear, thereby reducing system components and increasing reliability. The power output of the typical ISA is considerably less than the electric motors used in hybrid vehicles. Current ISA machines generally have capacities of about 2 kilowatts to 6 kilowatts, as compared to the 10 kilowatt or greater capacity in typical hybrid electric vehicles, and thus the ISA machines are generally not powerful enough to, nor designed to, accelerate a vehicle or provide “launch assist.”
There is a need for an improved combustion engine for incorporation into conventional vehicles. More particularly, there is a need for a combustion engine that has improved acceleration and efficiency with reduced emissions.